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This video shows the work currently underway on 4th Street between Bryant and Harrison streets in SoMa. The full HD video can be downloaded here.

It may look like a lot of dirt and mud right now, but in just a few years, what you see in the video above will become the Central Subway – a major upgrade to San Francisco’s public transportation system that will significantly improve mobility for thousands of San Franciscans.

The exciting first chapter of constructing the Central Subway tunnel is progressing in SoMa, with construction of a major excavation known as a launch box underway on 4th Street between Bryant and Harrison streets. At nearly 500 feet long, 50 feet wide and up to 40 feet deep, the launch box will take up most of the block.

Currently, tunneling contractor Barnard Impregilo Healy Joint Venture is using cranes and specialized excavators, including a 10-foot-tall, 15-ton, claw-like hydraulic excavator known as a “grab,” to dig a series of deep, narrow holes around the perimeter of the launch box. The holes, ranging in depth from 60 to 80 feet, are stabilized using a mud-like slurry and then backfilled with concrete to form panels. The panels will make up the walls of the tunnel launch box.

The 10-foot-tall, 15-ton “grab” shown here is digging a series of deep, narrow holes around the perimeter of the launch box. The holes are stabilized using a mud-like slurry and then backfilled with concrete to form panels, forming the walls of the tunnel launch box.

Next year two tunnel boring machines will start digging the Central Subway tunnels from the launch box, traveling north under 4th Street and then Stockton Street. The launch box will eventually become the portal where T Third Line trains will enter and exit the Central Subway tunnel, quickly transporting transit customers through SoMa, Union Square and Chinatown.

Here are a few more photos of the work currently underway to construct the Central Subway tunnel:

After using the grab to remove earth from the ground, the crane operator deposits it nearby. Later, the excavated materials will be transported off-site.

This large crane is used to excavate areas that are not beneath the I-80 overpass. A smaller crane (shown in the top photo) is used beneath the I-80 overpass.

These I-beams will be used to stabilize the walls around the launch box.